Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
  • H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
  • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
  • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
  • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
  • H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
  • H01S3/1001—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by controlling the optical pumping
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/29—Repeaters
  • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
  • H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
  • H04B10/2916—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing using Raman or Brillouin amplifiers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/06—Construction or shape of active medium
  • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
  • H01S3/067—Fibre lasers
  • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
  • H01S3/06725—Fibre characterized by a specific dispersion, e.g. for pulse shaping in soliton lasers or for dispersion compensating [DCF]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/06—Construction or shape of active medium
  • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
  • H01S3/067—Fibre lasers
  • H01S3/06754—Fibre amplifiers
  • H01S3/06758—Tandem amplifiers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
  • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
  • H01S3/094076—Pulsed or modulated pumping

Definitions

• the present invention relates to a Raman amplifier for intensity-modulating a signal at a high frequency of 100 MHz or higher and an optical communication system using the Raman amplifier.
• Patent Document 1 discloses that a Raman amplifier is more suitable than EDFA in order to modulate at a relatively high frequency.
• Patent Document 1 Japanese Patent Application Laid-Open No. 11-344732
• Patent Document 2 Japanese Patent Laid-Open No. 2001-311973
• Non-Patent Document 1 2002 IEICE Communication Society Conference B-10-107 “Examination of Gain Modulation Characteristics of Distributed Raman Amplifier Line” (Imai et al.)
• Patent Document 1 a modulation method using a conventional Raman amplifier generates a relatively low-speed supervisory control signal in an optical transmission system. It was only something to modulate. For this reason, the modulation frequency in the conventional Raman amplifier was relatively low, less than 10 MHz at most. Although these documents suggest the possibility of modulation at higher frequencies, Raman amplifiers that actually allow modulation at higher frequencies are disclosed.
• the present invention has been made in view of the above, and is a Raman amplifier for modulating a signal having a high frequency of 100 MHz or more, and has a small mounting volume and high reliability.
• An object of the present invention is to obtain a Raman amplifier having less polarization dependency and wavelength dependency of carrier light and less insertion loss of carrier light, and an optical communication system using the Raman amplifier.
• the present invention provides a Raman amplifier that amplifies carrier light using a Raman amplification medium.
• the Raman pumping light is intensity-modulated at a frequency of 100 MHz or more.
• An excitation light source to be supplied to the amplification medium; and multiplexing means for combining the carrier light and the excitation light to guide the Raman amplification medium to the Raman amplification medium.
• the Raman amplification medium has a low dispersion characteristic and has carrier light. It is a Raman amplification medium that has a small difference in transit time between the excitation light and the excitation light.
• the Raman amplifier according to the present invention employs a Raman amplification medium having low dispersion characteristics and a small difference in transit time between the carrier light and the pumping light, so that the signal is modulated by actively changing the gain.
• the intensity can be modulated at a frequency higher than lOOMHz.
• FIG. 1 is a configuration diagram illustrating a Raman amplifier according to a first embodiment.
• FIG. 2 is a diagram for explaining the relationship between the dispersion characteristic of an optical fiber and the upper limit of the modulation frequency.
• FIG. 3 is a configuration diagram illustrating a Raman amplifier according to a third embodiment.
• FIG. 4 is a configuration diagram illustrating a Raman amplifier according to a fourth embodiment.
• FIG. 5 is a diagram showing a configuration of an optical communication system to which the Raman amplifier of the present invention is applied. Explanation of symbols
• FIG. 1 is a configuration diagram illustrating the Raman amplifier according to the first embodiment.
• the Raman amplifier 1 according to the first embodiment includes a Raman amplification low dispersion optical fiber 2 that is a Raman amplification medium, a pumping LD (laser diode) 3 that is a pumping light source, and a pumping LD.
• LD drive and modulation circuit 4 to drive and modulate the LD light
• WD M Widelength
• 9 is a signal source of 100 MHz that gives a signal to the Raman amplifier 1.
• the carrier light input from the input terminal 6 is guided to the Raman amplification optical fiber 2 through the WDM multiplexer 5 and output from the output terminal 7.
• the WDM multiplexer 5 efficiently combines pumping light and carrier light having different wavelengths and guides them into the same optical fiber.
• the fiber fusion and extension type and the dielectric film filter type are used. The force that is used may be used.
• the LD drive and modulation circuit 4 drives the excitation LD3. Then, the intensity-modulated pumping light 8 is guided to the Raman amplification optical fiber 2 through the WDM multiplexer 5.
• the LD drive 'modulation circuit 4 may perform baseband modulation in which the signal from the signal source 9 is modulated as it is with an intensity corresponding to 0 or 1, or may be electrically connected to, for example, a higher frequency subcarrier carrier wave. Subcarrier modulation may be performed to modulate the excitation light after superimposing the signals.
• the gain given to the carrier light is modulated because the intensity of the pumping light is modulated. As a result, carrier light whose intensity is modulated is output from the output terminal 7.
• FIG. 1 shows a forward pumping configuration in which pumping light and carrier light propagate through the Raman amplification optical fiber 2 in the same direction. It is known from Non-Patent Document 1 that the forward excitation type is more suitable for modulation at a high frequency. Furthermore, in the present invention, in order to modulate the carrier light at a high frequency of 10 OMHz of the signal source 9, the optical fiber 2 for Raman amplification has a low dispersion characteristic, which allows the propagation propagation of the carrier light and the pump light. The time difference is made small.
• the rise time 13 of the modulated carrier light is about several ns. That is what you need.
• the modulation frequency is further increased, period 11 is shortened, but rise time 13 is not changed. Since the fall time takes about the same time as the rise time, the upper limit of the modulation frequency is when the sum of the rise time and fall time and the period 11 match.
• the rise and fall times that determine the upper limit of the modulation frequency are passed according to the wavelength difference between the carrier light and the pump light, depending on the dispersion characteristics of the Raman amplification optical fiber 2. This is caused by a difference in over-propagation time.
• the carrier light and the pump light that are simultaneously incident on the Raman amplification optical fiber 2 have a time difference when output from the output end 7 of the optical fiber 2 due to the dispersion characteristics of the Raman amplification optical fiber 2.
• the intensity of the carrier light is modulated while propagating, but due to a time lag between the carrier light and the pumping light, the modulation waveform becomes dull and a finite rise is caused.
• a rise time occurs.
• this rise time is shortened, and thereby a modulation at a higher frequency than ever before is performed by a Raman amplifier. It is possible with.
• lZl6ns 63MHz is a guideline for the upper limit of the modulation frequency. Under this condition, carrier light cannot be modulated at a frequency of 100MHz.
• the length of the optical fiber for Raman amplification is 6. lkm
• the wavelengths of the carrier light and the pumping light are 1550 nm and 1450 nm, respectively
• the absolute value of the dispersion value of the optical fiber 2 is
• the carrier light can be modulated by the signal source 9 having a frequency of lOOMHz.
• Patent Document 2 discloses a Raman amplifier that amplifies light with a constant gain without fluctuation, eliminating the influence of noise of the pumping light source, and therefore an optical fiber having a small dispersion value. I use a bar.
• the optical fiber 2 having a small dispersion value is used in order to positively modulate the intensity of the carrier light using the excitation light that has been intensity-modulated at a high frequency.
• both use the same optical fiber with a small dispersion value, but the former does not have the viewpoint of actively changing the amplified light.
• the Raman amplification optical fiber 2 having a small dispersion value is provided. Since it was used to perform Raman amplification, it is possible to modulate a signal with a high frequency of 100 MHz or higher.
• the Raman gain coefficient of the optical fiber used in the measurement of FIG. 2 is 2.5 / W / m, which is relatively higher than that of a normal optical fiber, but an optical fiber having a higher gain coefficient should be used.
• the effect of increasing the upper limit of the modulation speed can be obtained.
• the larger the gain factor the higher the gain obtained with the same pumping light intensity and the same optical fiber length.
• the carrier light can be intensity-modulated with a short optical fiber length, so that the propagation delay time in the optical fiber can be reduced.
• the upper limit of the modulation frequency is
• the effect of further increasing the upper limit of the modulation frequency can be obtained by using an optical fiber having a high Raman gain coefficient as well as using an optical fiber having a small absolute value of dispersion.
• the shortening of the optical fiber 2 has the effect of reducing the size of the Raman amplifier 1. Furthermore, since there is an effect of reducing the loss of carrier light in the Raman amplifier 1, there is also an effect that a low-loss modulator can be obtained.
• the excitation light source 3 employed in Embodiment 1 is a laser diode having a wavelength of 1450 nm. For this, a highly reliable laser diode that has been proven in an EDFA submarine repeater can be used. Further, by using a redundant configuration using a plurality of pump laser diodes as the pump light source 3, higher reliability can be obtained. Also, WDM multiplexer 5 and Raman amplification light Since the fiber 2 is a passive component that can be relatively easily increased in reliability, the Raman amplifier 1 is a highly reliable Raman amplifier that modulates the carrier light. Since the Raman amplifier can easily reduce the polarization dependence of the gain, it becomes an amplifier having a small polarization dependence.
• the Raman amplifier has a wide gain band and a small wavelength dependency of the gain, so that the amplifier has a small wavelength dependency.
• an amplifier having these advantages is used to modulate observation signals from observation devices such as seismometers, tsunami meters, thermometers, and cameras installed on the sea floor into carrier light.
• observation devices such as seismometers, tsunami meters, thermometers, and cameras installed on the sea floor into carrier light.
• a highly reliable remote seafloor observation system can be realized by transmitting to the receiver installed on land via the seafloor cable.
• FIG. 3 is a block diagram showing a Raman amplifier according to the third embodiment of the present invention.
• the optical fiber 2 for Raman amplification has a configuration in which an optical fiber 2a having a positive dispersion characteristic and an optical fiber 2b having a negative dispersion characteristic are alternately connected.
• Other configurations are the same as in Fig. 1.
• FIG. 4 is a block diagram showing a Raman amplifier according to the fourth embodiment of the present invention.
• Embodiment 4 shown in FIG. 4 has a configuration in which the Raman amplifiers in FIG. 1 are cascaded in two stages.
• the wavelengths of the carrier light and the pump light are 1550 nm and 1450 nm, respectively
• the dispersion value of the Raman amplification optical fiber 2 is 16 ps / nm / km.
• Each length of the two optical fibers 2 is 3 km, which is half of the length of the first embodiment.
• the modulation amplitude of the carrier light obtained by one Raman amplification optical fiber 2 is halved, but by being modulated by two optical fibers 2, the embodiment is realized.
• a sufficient modulation amplitude can be obtained in the same manner as in state 1.
• the upper limit of the modulation speed is
• FIG. 5 is a configuration diagram showing an optical communication system using any of the Raman amplifiers according to the first to fourth embodiments of the present invention.
• This optical communication system includes a transmitting device 100 that transmits wavelength-multiplexed carrier light, a receiving device 101 that receives wavelength-multiplexed carrier light, an optical fiber mirror 102, a repeater 103, and an observation device 104.
• the observation device 104 includes the Raman amplifier 1 described in any of Embodiments 1 to 4, a data processing unit 105, and observation units 106 such as a seismometer, a tsunami meter, a thermometer, and a camera.
• Wavelength multiplexed carrier light transmitted from a transmitter 100 installed on land propagates through an optical fiber cable 102, which is a submarine cable, and passes through a repeater 103 that compensates for propagation loss in the optical fiber cable 102.
• the observation device 104 installed on the ocean floor.
• the observation device 104 is equipped with observation devices 106 such as seismometers, tsunami meters, thermometers, cameras, etc., and these observation signals require D / A conversion, multiplexing, subcarrier modulation, etc.
• the carrier light having a part of the wavelength is modulated by the Raman amplifier 1.
• the wavelength multiplexed carrier light transmitted from the observation device 104 passes through the optical fiber cable 102 and the repeater 103 to the reception device 101 installed on the land.
• the Raman amplifier 1 can be realized with a high level of reliability and is suitable for a submarine cable system that requires high reliability.
• characteristics such as small size, low loss, low polarization dependency, and low wavelength dependency are characteristics that are suitable for realizing a seafloor remote observation system.
• the pump light has a wavelength of 1450 nm and the carrier light has a wavelength of 1550 nm as an example. Excitation light having another wavelength suitable for this may be used.
• the modulation frequency is not limited to 100 MHz, but any frequency above 100 MHz may be used.
• the Raman amplification medium other means suitable for Raman amplification such as an optical fiber based on tellurite may be used. You can use Raman amplification media.
• the Raman amplifier according to the present invention is useful for an optical modulator for modulating a signal having a high frequency of 100 MHz or more, and particularly for observation of a seismometer, a tsunami meter, a thermometer, a camera, and the like. This is suitable for Raman amplifiers used in remote observation systems at the bottom of the ocean that modulate the excitation light using the signal from the center.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
• Optical Communication System (AREA)

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• 2004
  • 2004-08-30 EP EP04772458A patent/EP1788426B1/de not_active Expired - Lifetime
  • 2004-08-30 WO PCT/JP2004/012502 patent/WO2006025095A1/ja active Application Filing
  • 2004-08-30 US US11/661,502 patent/US7768698B2/en active Active - Reinstated
  • 2004-08-30 CA CA2577476A patent/CA2577476C/en not_active Expired - Fee Related
  • 2004-08-30 JP JP2006531203A patent/JP4809770B2/ja not_active Expired - Fee Related

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